Field of the Invention
The present invention relates to a technique of measuring the three-dimensional shape of a target object.
Description of the Related Art
There is widely known a three-dimensional shape measurement apparatus that obtains a three-dimensional coordinate by the triangulation principle based on a striped pattern typified by binary or Gray code structured light or a phase shift, or the observation position of reflected light of light projected to a target object in an image capturing unit. This apparatus may not obtain desired measurement accuracy upon a change of the geometric relation between the three-dimensional shape measurement apparatus and a target object owing to the vibration of a structure supporting the apparatus. Also, the apparatus may not obtain desired measurement accuracy upon a change of the position of a pattern or laser spot projected to a target object owing to the temporal fluctuation of the geometric relation between the image capturing unit and the projection unit. To solve these problems, for example, Japanese Patent Laid-Open No. 8-54234 (patent literature 1) has proposed a method of measuring a reference object that is arranged together with a target object and has a known true value of the distance, and correcting the position coordinate of spot light based on a shift of the light projection angle of a mirror and a shift of the image capturing angle from reference states. Japanese Patent Laid-Open No. 5-248830 (patent literature 2) has proposed a method of splitting beam light by a splitter, observing the temporal fluctuation of the beam light by a position detection device for correction, and correcting a measured value.
The fluctuation of the geometric relation between the three-dimensional shape measurement apparatus and a target object due to the vibration of the support structure, and the fluctuation of the position of a pattern or laser spot projected to the target object occur independently, but are interdependent in general. In other words, these two fluctuations are observed while being influenced mutually. For example, even if a pattern shift is corrected by the method described in patent literature 2, an error arising from the vibration of the three-dimensional shape measurement apparatus cannot be completely removed. In the method described in patent literature 1, a measured value itself used for correction has an error at the stage of triangulation under the influence of the temporal fluctuation of projected light. Even by using a measured value based on triangulation, the error of the motion amount of the entire apparatus cannot be completely corrected. Even by simultaneously applying a plurality of methods premised on that only one of these two fluctuations occurs, as in the above-mentioned methods, an error remains to a certain extent, and no satisfactory measurement accuracy can be obtained.